What app allows you to download free unlimited music on your iPhone 4s?

I'm really desperate. I don't know what to do. I've been searching for a free app for music, but I just, simply can't find one!
It has to be free, and allowing me to download an unlimited amount of music…
If not unlimited, then at least 40 tracks… Please…

There's no such thing. It may be inconvenient, but it's only fair to pay for it. Music costs money to produce, market, pay the artists. Think of it this way… Would you do a job that you don't get paid for? You can listen on Pandora or iTunes radio for free, but unlimited free music downloads… No chance.